#    This program is free software: you can redistribute it and/or modify
#    it under the terms of the GNU General Public License as published by
#    the Free Software Foundation, either version 3 of the License, or
#    (at your option) any later version.
#
#    This program is distributed in the hope that it will be useful,
#    but WITHOUT ANY WARRANTY; without even the implied warranty of
#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#    GNU General Public License for more details.
#
#    You should have received a copy of the GNU General Public License
#    along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
#    Code base of Animesh Sharma [ sharma.animesh@gmail.com ]

sub factorial {
    my $number = shift @_;
    return undef if $number < 0; # illegal value
    return 1 if $number == 0;

    my $factorial = 1;
    for (my $i = $number; $i > 1; $i--) {
	$factorial = $factorial * $i;
    }
    return $factorial;
}
